Customer has two story, 2 zone home with a BMPPlus3000.
Complaint is a blower fan clunk when the air conditioner turns on, which I verified.
The clunk happens because the fan on the Lennox gas furnace switches from low speed to high speed when the AC starts up. Thermostats are working fine, Lennox system is fine.
The problem is with the EWC panel. When either thermostat calls for cooling, the zoning panel activates the fan relay (green) several seconds before the cooling relay (yellow) is activated. The causes the furnace to start the fan in low speed mode, then switch the fan off for two seconds while the compressor starts, then turn the fan to high speed mode.
Is this a broken zone controller (stuck cooking relay?) or is there a way to get both cooling and fan relays to close simultaneously like the furnace is expecting?
Customer complaint -Fan Clunk on air conditioner startup
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Pcyrana
Re: Customer complaint -Fan Clunk on air conditioner startup
The BMPlus3000 does not appear to be defective. On a call for cooling the board will energize the Fan for 5 seconds before it energizes the Compressor. This is done to ensure that no liquid refrigerant enters the Compressor upon start-up. Before I can assist you further on what the problem might be, I am going to need more information on your application. What type of Blower motor are you running? Is it a PSC (Permanent Split Capacity) or a Variable Speed Blower Motor? Also, can you tell me the exact model number of the thermostats you are using in each zone?
Re: Customer complaint -Fan Clunk on air conditioner startup
So, it sounds like the Lennox furnace is expecting a "dumb" thermostat to be hooked up to it directly, which would activate the compressor and the fan simultaneously when the thermostat clicks.
EWC is trying to be smarter by blowing the fan over the evap coils a little before activating the compressor to make sure any liquid refrigerant still in the coil from the last cycle is evaporated. I admit, a good idea to extend the life of the compressor (except maybe in this case).
The way the Lennox G51 furnace actually works is that it starts the compressor two seconds before activating the indoor blower. The furnace is a mid-grade gas furnace with four speed taps for the blower (high speed = cool, #2 speed = heat, low speed is the blower-only), it is not variable speed. So, when using the EWC zoning panel, what happens is that the blower turns on low speed mode and begins to get up to speed. Then, the cooling relay closes causing power to the fan to shut off for two seconds. Then, the fan is again turned on at high speed.
The rapid on/off/on cycle of the blower is making an audible thunk in the customer's family room (directly above the unit). Can't be too good for the health of the fan either. Don't get me wrong, it is not unreasonably loud, and it doesn't sound like the fan is bad... but it is annoying.
The existing thermostats that you asked about are basic grade non-programmable White Rodgers that the customer had intended on replacing with VisionPro models.
Any suggestions? Is there any way to change the 5 second fan-compressor delay?
EWC is trying to be smarter by blowing the fan over the evap coils a little before activating the compressor to make sure any liquid refrigerant still in the coil from the last cycle is evaporated. I admit, a good idea to extend the life of the compressor (except maybe in this case).
The way the Lennox G51 furnace actually works is that it starts the compressor two seconds before activating the indoor blower. The furnace is a mid-grade gas furnace with four speed taps for the blower (high speed = cool, #2 speed = heat, low speed is the blower-only), it is not variable speed. So, when using the EWC zoning panel, what happens is that the blower turns on low speed mode and begins to get up to speed. Then, the cooling relay closes causing power to the fan to shut off for two seconds. Then, the fan is again turned on at high speed.
The rapid on/off/on cycle of the blower is making an audible thunk in the customer's family room (directly above the unit). Can't be too good for the health of the fan either. Don't get me wrong, it is not unreasonably loud, and it doesn't sound like the fan is bad... but it is annoying.
The existing thermostats that you asked about are basic grade non-programmable White Rodgers that the customer had intended on replacing with VisionPro models.
Any suggestions? Is there any way to change the 5 second fan-compressor delay?
-
Pcyrana
Re: Customer complaint -Fan Clunk on air conditioner startup
Does your customer like to run continuous fan at anytime during the heating the cooling season? If not you could disconnect the "G" from the system terminal block going to the equipment. This would disable the option to run fan only from any thermostat but it will also eliminate the "clunk" you hear when initiating a cooling call. Let me know how that works out for you.